Exactly what subject states what's the difference between the two? Lifetime? And also on my u joint there was a flat metal that kinda went acrossed it and and like broke off it was thin and about 2 in long I'd say?

Exactly what subject states what's the difference between the two? Lifetime? And also on my u joint there was a flat metal that kinda went acrossed it and and like broke off it was thin and about 2 in long I'd say?

The difference, how much you pay for them.
The metal piece is only there to hold the caps on when the driveshaft is removed ( unbolted ) from the pinion yoke. No more no less.